Diamond is a solid form of the element carbon with its atoms arranged in a crystal structure called diamond cubic. At room temperature and pressure, another solid form of carbon known as graphite is the chemically stable form of carbon, but... Wikipedia Density: 3.51 g/cm³ Formula mass: 12.01 g/mol Crystal habit: Octahedral Crystal class: Hexoctahedral (m3m); H-M symbol: (4/m 3 2/m)